Enzymes and Inhibitors involved in the proteolysis of lung and its control are being investigated in order to determine their role in the development of emphysema. It is suggested that by investigating the structure of both the inhibitors and the enzymes it should be possible to develop synthetic inhibitors which could prove useful in therapy for individuals who have early signs of chronic obstructive lung disease. Two sources of the enzymes, leukocytes and macrophages, are being examined in order to find whether other proteinases may be involved in the uncontrolled digestion of lung tissue.